The present invention relates to an inverter unit which has a pair of circuit boards arranged at a predetermined space to face each other.
Japanese Unexamined Patent Publication No. 2000-133768 discloses a power semiconductor module. The power semiconductor module includes an insulating metal substrate in which a metal plate, an insulating layer and copper foil patterns are laminated in this order. The copper foil patterns include a main circuit pattern area having power semiconductor devices such as IGBTs (Insulated Gate Bipolar Transistor) and a control circuit pattern area having control semiconductor devices. The main circuit pattern area and the control circuit pattern area are separated from each other by a linear separator.
In the above-described power semiconductor module wherein the main circuit pattern area having power semiconductor devices and the control circuit pattern area having control semiconductor devices are separated from each other by the linear separator, the noise developed by the switching of the power semiconductor devices can be suppressed from transmitting to the control semiconductor devices through the metal plate.
There has been an increasing demand for downsizing and increasing the output power of inverter units as a semiconductor module. To meet such demand, it is proposed that circuit components of the inverter unit including a plurality of power devices, a plurality of capacitors and control devices should be arranged separately on a plurality of circuit boards and such circuit boards should be arranged at a predetermined space from each other. In such an inverter unit, large current flows in the main circuit including the power devices and the capacitors while relatively small current flows in the control circuit including the control devices controlling the switching of the main circuit as compared to the current in the main circuit. Though the parts of an inverter unit have different sizes and shapes, mixed arrangement of parts for the main circuit and parts for the control circuit on a single circuit board of the inverter unit may enhance the mounting density of parts and realize downsizing of the inverter unit.
However, the above-described inverter units have problems that noise occurs during the switching of the power devices and high heat generation occurs due to large current flowing in the main circuit. Therefore, transmission of noise and heat to the control circuit of the inverter unit need be suppressed.
The present invention is directed to providing an inverter unit that suppresses the influence of the noise development of power devices and the heat generation of the main circuit on the control circuit of the inverter unit.